Recently, in a multilayer polishing process, a dual damascene process and the like of an integrated circuit, a CMP (Chemical Mechanical Polishing) process is mainly used for global planarization on the wafer surface. The CMP process is a polishing method for planarizing the wafer surface chemical-mechanically using a polishing pad and slurry when manufacturing a semiconductor, and in this process, the slurry composition is dropped on the polishing pad made of polyurethane and then contacted with the wafer followed by subjecting the wafer to orbital movement combining rotation and translation.
In the CMP process, the slurry generally comprising polishing agents (abrasives) for physical polishing effect and active ingredients (for example, etchants or oxidants) for chemical polishing effect allows any protrusion of the wafer surface to be selectively etched physicochemically, resulting in planarization of the wafer.
According to the polishing subject, the CMP slurry can be classified into insulating layer polishing slurry and metal polishing slurry. The insulating layer polishing slurry can be applied to a ILD (interlayer dielectric) process or a STI (Shallow trench isolation) process in a semiconductor process, and the metal polishing slurry can be applied to form interconnects of tungsten, aluminum or copper wires and tungsten contacts/via plug, or to a dual damascene process.
FIG. 1 shows a flow chart of a process manufacturing a semiconductor device to which the tungsten CMP slurry composition according to the present invention is applied.
in the process for manufacturing a flash memory device according to one embodiment of the present invention, first of all, as shown in FIG. 1, a SiO2 oxide film is formed on a semiconductor substrate, a silicon substrate equipped with some structures such as, a gate electrode, a source plug contact region and a drain plug contact region to the thickness of 1000 to 2000 Å, and then the SiO2 oxide film is etched to expose the source plug contact region so as to form a contact hole.
Then, as shown in FIG. 1, a tungsten (W) film is deposited on the entire surface to completely fill up the contact hole. In order to enhance adhesiveness of the tungsten film with the SiO2 oxide film and a nitride film, an adhesive layer made of Ti is formed on the surface of the semiconductor substrate before depositing the tungsten film, and a barrier metal film made of TiN is further formed on the adhesive layer to prevent bonding between WF6 (source material) and highly reactive Ti when forming the tungsten film. Subsequently, as the first CMP process using the metal slurry, the tungsten film on the SiO2 oxide film is polished to form a tungsten plug in the contact hole. After completing the first CMP process, oxidative defects caused by chemical reaction between hydrogen peroxide (H2O2) solution and the metal slurry are severely occurred on the tungsten plug of the semiconductor substrate.
Then, in order to remove the oxidative defects, the second soft CMP process is conducted by using oxide slurry for several seconds to several minutes resulting in removing the oxidative defects on the tungsten plug and polishing the SiO2 oxide film to a certain thickness.
In the said process for manufacturing a semiconductor device, the slurry for the first metal polishing slurry generally comprises abrasives, oxidants, auxiliary oxidants, dispersing agents, pH controlling agents, other additives and the like. Among the said ingredients, the abrasives are for mechanical polishing, the oxidants and the auxiliary oxidants are for promoting polishing through oxidation of the metal layer, the dispersing agents are for enhancing dispersion stability of the slurry, the pH controlling agents are for controlling pH range in which oxidation could occur well according to properties of the metal layer as a polishing subject, and other additives are for improving or complementing performance of the slurry.
The tungsten CMP process uses slurry containing the oxidants, and generally, strong oxidants such as hydrogen peroxide (H2O2) and iron nitrate (Fe(NO3)3) are mixed with the slurry containing abrasives such as silica and alumina minute particles. The oxidants in the slurry oxidize the tungsten surface to tungsten oxide (WO3), which can be easily removed with the abrasives because it is weaker than W. In the tungsten CMP process, processes removing WO3 with the abrasives in the slurry and the CMP pad for mechanical polishing, oxidizing the metal W under the WO3 layer to WO3 by the oxidants, and removing thereof are repeated to remove the tungsten film. And the metal barrier film can be removed by similar mechanism with the tungsten polishing.
In the metal CMP process, a process removing the oxides formed by the oxidants with the abrasive particles is conducted repeatedly. Therefore, in order to enhance polishing rate, the oxidation process should be conducted faster, or the slurry should be designed in consideration of smoothly removing the formed oxides.
With ease, there is a method to enhance the polishing rate by increasing the concentration of the oxidants corroding metals, but it may decrease reliability and yield of a device because erosion even occurs at a part, where a wiring layer should be formed for electrical properties of the device, such as corrosion pit or contact parts according to the increase of erosion rate.
The metal polishing slurry should have difference in the polishing rates in the metal layer and the insulating layer. Therefore, higher polishing rate is needed in a metal wire, and lower polishing rate is needed in the insulating layer. If the rate difference is low, defects such as erosion may occur at parts where pattern density is high because the polishing rate is partially increased only at parts where the pattern density is high. Therefore, the polishing rate in the insulating layer should become lower to prevent partial increase of the polishing rate.
Now, CMP slurry containing iron nitrate is widely used. For example, Korean Patent No. 10-0745447 by Cabot discloses a chemical and mechanical polishing precursor composition comprising: catalysts having multiple oxidation states, which are mixed with oxidants and useful for removing a metal layer from a substrate; and stabilizers, and the used catalysts contains iron.
However, the conventional slurry containing strong oxidants act directly on the tungsten surface resulting in causing strong oxidation. Therefore, because its tungsten film removing rate to its interlayer insulating film removing rate, i.e., polishing selectivity, is very high as 50 to 150, there are problems that excessive plug recess may occur, and roughness of the plug surface after completing CMP may become high. Further, when a metal catalyst comprising iron nitrate is used, there is a problem of occurring pad contamination caused by discoloration. Accordingly, development of CMP slurry, which can improve the problems, is needed.